Note: Descriptions are shown in the official language in which they were submitted.
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LIQUEFIED NATURAL GAS PRODUCTION
CROSS-REFERENCE TO RELATED APPLICATION
100011 This application claims the benefit of U.S. Provisional Patent
Application 61/756,322
filed 24 January 2013 entitled LIQUEFIED NATURAL GAS PRODUCTION.
FIELD OF THE INVENTION
[00021 The present techniques relate generally to the field of
hydrocarbon recovery and
treatment processes and, more particularly, to a method and systems for
liquefied natural gas
(LNG) production via a refrigeration process that uses mixed fluorocarbon
refrigerants.
BACKGROUND
[0003] This section is intended to introduce various aspects of the art,
which may be
associated with exemplary embodiments of the present techniques. This
discussion is believed to
assist in providing a framework to facilitate a better understanding of
particular aspects of the
present techniques. Accordingly, it should be understood that this section
should be read in this
light, and not necessarily as admissions of prior art.
[0004] Many low temperature refrigeration systems that are used for
natural gas processing
and liquefaction rely on the use of single component refrigerants or mixed
refrigerants (MRs)
including hydrocarbons components to provide external refrigeration. For
example, liquefied
natural gas (LNG) may be produced using a mixed refrigerant including
hydrocarbon
components extracted from a feed gas. Such hydrocarbon components may include
methane,
ethane, ethylene, propane, and the like.
100051 U.S. Patent No. 6,412,302 to Foglietta et al. describes a process
for producing a
liquefied natural gas stream. The process includes cooling at least a portion
of a pressurized
natural gas feed stream by heat exchange contact with first and second
expanded refrigerants that
are used in independent refrigeration cycles. The first expanded refrigerant
is selected from
methane, ethane, and treated and pressurized natural gas, while the second
expanded refrigerant
is nitrogen. Therefore, such techniques rely on the use of refrigerants
including hydrocarbons,
which are flammable.
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[00061 U.S. Patent Application Publication No. 2010/0281915 by Roberts
et al. describes a
system and method for liquefying a natural gas stream. A dehydrated natural
gas stream is pre-
cooled in a pre-cooling apparatus that uses a pre-coolant consisting of a HFC
refrigerant. The
pre-cooled dehydrated natural gas stream is then cooled in a main heat
exchanger through
indirect heat exchange against a vaporized hydrocarbon mixed refrigerant
coolant to produce
LNG. The mixed refrigerant coolant includes ethane, methane, nitrogen, and
less than or equal
to 3 mol % of propane. Therefore, such techniques also rely on the use of
refrigerants including
hydrocarbons.
100071 U.S. Patent Application Publication No. 2012/0047943 by Barclay
et al. describes a
process for offshore liquefaction of a natural gas feed. The process includes
contacting the
natural gas feed with a biphasic refrigerant at a first temperature,
contacting the natural gas feed
with a first gaseous refrigerant at a second temperature, and contacting the
natural gas feed with
a second gaseous refrigerant at a third temperature. The refrigerated natural
gas feed is then
expanded using an expansion device to form a flash gas stream and a liquefied
natural gas
stream. The biphasic refrigerant may be a commercial refrigerant such as R507
or R134a, or a
mixture thereof. The first gaseous refrigerant may be nitrogen. The second
gaseous refrigerant
may be the flash gas stream recovered from the natural gas feed. The biphasic
refrigerant is used
to cool and partially condense the natural gas feed in a feed gas chiller,
while the first and second
gaseous refrigerants are used to cool and condense the natural gas feed in a
main cryogenic heat
exchanger. Therefore, such techniques rely on the use of a refrigerant
including hydrocarbon
components extracted from the natural gas feed.
[00081 U.S. Patent No. 6,631,625 to Weng describes a non-
hydrochlorofluorocarbon (non-
HCFC) design of a refrigerant mixture for an ultra-low temperature
refrigeration system. The
non-HCFC refrigerant mixture is primarily composed of hydrofluorocarbon (HFC)
refrigerants
and hydrocarbons. Therefore, such techniques also rely on the use of
refrigerants including
hydrocarbons. Furthermore, the use of such refrigerant mixtures for natural
gas processing or
liquefaction is not disclosed.
SUMMARY
100091 An embodiment provides a hydrocarbon processing system for
liquefied natural gas
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(LNG) production. The hydrocarbon processing system includes a fluorocarbon
refrigeration
system configured to cool a natural gas to produce LNG using a mixed
fluorocarbon refrigerant
and a nitrogen rejection unit (NRU) configured to remove nitrogen from the
LNG.
[00101 Another embodiment provides a method for liquefied natural gas
(LNG) production.
The method includes cooling a natural gas to produce LNG in a fluorocarbon
refrigeration
system using a mixed fluorocarbon refrigerant and removing nitrogen from the
LNG in a
nitrogen rejection unit (NRU).
[00111 Another embodiment provides a hydrocarbon processing system for
the formation of
a liquefied natural gas (LNG). The hydrocarbon processing system includes a
mixed refrigerant
cycle configured to cool a natural gas using a mixed fluorocarbon refrigerant,
wherein the mixed
refrigerant cycle includes a heat exchanger configured to allow for cooling of
the natural gas via
an indirect exchange of heat between the natural gas and the mixed
fluorocarbon refrigerant.
The hydrocarbon processing system also includes a nitrogen rejection unit
(NRU) configured to
remove nitrogen from the natural gas and a methane autorefrigeration system
configured to cool
the natural gas to produce the LNG.
BRIEF DESCRIPTION OF THE DRAWINGS
[00121 The advantages of the present techniques are better understood by
referring to the
following detailed description and the attached drawings, in which:
[00131 Fig. 1 is a process flow diagram of a single stage refrigeration
system;
[00141 Fig. 2 is a process flow diagram of a two stage refrigeration system
including an
economizer;
100151 Fig. 3 is a process flow diagram of a single stage refrigeration
system including a heat
exchanger economizer;
[00161 Fig. 4 is a process flow diagram of a liquefied natural gas (LNG)
production system;
[00171 Fig. 5 is a process flow diagram of a hydrocarbon processing system
including a
single mixed refrigerant (SMR) cycle;
[00181 Fig. 6 is a process flow diagram of the hydrocarbon processing
system of Fig. 5 with
the addition of a nitrogen refrigeration system;
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[00191 Fig. 7 is a process flow diagram of the hydrocarbon processing
system of Fig. 5 with
the addition of a methane autorefrigeration system;
[00201 Fig. 8 is a process flow diagram of a hydrocarbon processing
system including a pre-
cooled SMR cycle;
100211 Fig. 9 is a process flow diagram of a hydrocarbon processing system
including a dual
mixed refrigerant (DMR) cycle;
[00221 Figs. 10A and 10B are process flow diagrams of a hydrocarbon
processing system
including an SMR cycle, an NRU, and a methane autorefrigeration system;
[00231 Figs. 11A and 11B are process flow diagrams of a hydrocarbon
processing system
including an economized DMR cycle, an NRU, and a methane autorefrigeration
system; and
[00241 Fig. 12 is a process flow diagram of a method for the formation
of LNG from a
natural gas stream using a mixed fluorocarbon refrigerant.
DETAILED DESCRIPTION
[00251 In the following detailed description section, specific
embodiments of the present
techniques are described. However, to the extent that the following
description is specific to a
particular embodiment or a particular use of the present techniques, this is
intended to be for
exemplary purposes only and simply provides a description of the exemplary
embodiments.
Accordingly, the techniques are not limited to the specific embodiments
described herein, but
rather, include all alternatives, modifications, and equivalents falling
within the spirit and scope
of the appended claims.
[00261 At the outset, for ease of reference, certain terms used in this
application and their
meanings as used in this context are set forth. To the extent a term used
herein is not defined
herein, it should be given the broadest definition persons in the pertinent
art have given that term
as reflected in at least one printed publication or issued patent. Further,
the present techniques
are not limited by the usage of the terms shown herein, as all equivalents,
synonyms, new
developments, and terms or techniques that serve the same or a similar purpose
are considered to
be within the scope of the present claims.
100271 As used herein, "autorefrigeration" refers to a process whereby a
portion of a product
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stream is used for refrigeration purposes. This is achieved by extracting a
fraction of the product
stream prior to final cooling for the purpose of providing refrigeration
capacity. This extracted
stream is expanded in a valve or expander and, as a result of the expansion,
the temperature of
the stream is lowered. This stream is used for cooling the product stream in a
heat exchanger.
After exchanging heat, this stream is recompressed and blended with the feed
gas stream. This
process is also known as open cycle refrigeration.
[0028] Alternatively, "autorefrigeration" refers to a process whereby a
fluid is cooled via a
reduction in pressure. In the case of liquids, autorefrigeration refers to the
cooling of the liquid
by evaporation, which corresponds to a reduction in pressure. More
specifically, a portion of the
liquid is flashed into vapor as it undergoes a reduction in pressure while
passing through a
throttling device. As a result, both the vapor and the residual liquid are
cooled to the saturation
temperature of the liquid at the reduced pressure. For example, according to
embodiments
described herein, autorefrigeration of a natural gas may be performed by
maintaining the natural
gas at its boiling point so that the natural gas is cooled as heat is lost
during boil off. This
process may also be referred to as "flash evaporation."
[00291 The "boiling point" or "BP" of a substance is the temperature at
which the vapor
pressure of the liquid equals the pressure surrounding the liquid and, thus,
the liquid changes into
a vapor. The "normal boiling point" or "NBP" of a substance is the boiling
point at a pressure of
one atmosphere, i.e., 101.3 kilopascals (kPa).
100301 A "compressor" includes any unit, device, or apparatus able to
increase the pressure
of a stream. This includes compressors having a single compression process or
step, or
compressors having multi-stage compression processes or steps, more
particularly multi-stage
compressors within a single casing or shell. Evaporated streams to be
compressed can be
provided to a compressor at different pressures. For example, some stages or
steps of a
hydrocarbon cooling process may involve two or more refrigerant compressors in
parallel, series,
or both. The present techniques are not limited by the type or arrangement or
layout of the
compressor or compressors, particularly in any refrigeration cycle.
[00311 As used herein, "cooling" broadly refers to lowering and/or
dropping a temperature
and/or internal energy of a substance, such as by any suitable amount. Cooling
may include a
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temperature drop of at least about 1 C, at least about 5 C, at least about
10 C, at least about 15
C, at least about 25 C, at least about 50 C, at least about 100 C, and/or
the like. The cooling
may use any suitable heat sink, such as steam generation, hot water heating,
cooling water, air,
refrigerant, other process streams (integration), and combinations thereof.
One or more sources
of cooling may be combined and/or cascaded to reach a desired outlet
temperature. The cooling
step may use a cooling unit with any suitable device and/or equipment.
According to one
embodiment, cooling may include indirect heat exchange, such as with one or
more heat
exchangers. Heat exchangers may include any suitable design, such as shell and
tube, brazed
aluminum, spiral wound, and/or the like. In the alternative, the cooling may
use evaporative
(heat of vaporization) cooling, sensible heat cooling, and/or direct heat
exchange, such as a
liquid sprayed directly into a process stream.
[0032] "Cryogenic temperature" refers to a temperature that is about ¨50
C or below.
f00331 As used herein, the terms "deethanizer" and "demethanizer" refer
to distillation
columns or towers that may be used to separate components within a natural gas
stream. For
example, a demethanizer is used to separate methane and other volatile
components from ethane
and heavier components. The methane fraction is typically recovered as
purified gas that
contains small amounts of inert gases such as nitrogen, CO2, or the like.
f00341 "Fluorocarbons," also referred to as "perfluorocarbons" or
"PFCs," are molecules
including F and C atoms. Fluorocarbons have F-C bonds and, depending on the
number of
carbon atoms in the species, C-C bonds.
An example of a fluorocarbon includes
hexafluoroethane (C2F6). "Hydrofluorocarbons" or "HFCs" are a specific type of
fluorocarbon
including H, F, and C atoms. Hydrofluorocarbons have H-C and F-C bonds and,
depending on
the number of carbon atoms in the species, C-C bonds. Some examples of
hydrofluorocarbons
include fluoroform (CHF3), pentafluoroethane (C2HF5), tetrafluoroethane
(C2H2F4),
heptafluoropropane (C3HF7), hexafluoropropane (C3H2F6), pentafluoropropane
(C3H3F5), and
tetrafluoropropane (C3H4F4), among other compounds of similar chemical
structure.
Hydrofluorocarbons with unsaturated bonds are referred to as
"hydrofluoroolefins" or "HFOs."
HFOs are typically more reactive and flammable than HFCs due to the presence
of unsaturated
bonds. However, HFOs also typically degrade in the environment faster than
HFCs.
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[00351 The term "gas" is used interchangeably with "vapor," and is
defined as a substance or
mixture of substances in the gaseous state as distinguished from the liquid or
solid state.
Likewise, the term "liquid" means a substance or mixture of substances in the
liquid state as
distinguished from the gas or solid state.
100361 The term "greenhouse gases" broadly refers to gases or vapors in an
atmosphere that
can absorb and/or emit radiation within the thermal infrared range. Examples
include carbon
monoxide, carbon dioxide, water vapor, methane, ethane, propane, ozone,
hydrogen sulfide,
sulfur oxides, nitrogen oxides, halocarbons, chlorofluorocarbons, or the like.
Electrical power
plants, petroleum refineries, and other energy conversion facilities can tend
to be large sources of
greenhouses gases emitted to the atmosphere. Without being bound by theory,
greenhouse gases
are believed to receive and/or retain solar radiation and energy, which become
trapped in the
atmosphere. This may result in an increase in average global atmospheric
temperatures and
other climate changes.
10371 The "global-warming potential" or "GWP" of a gas is a relative
measure of how
much heat the gas traps in the atmosphere. GWP compares the amount of heat
trapped by a
certain mass of the gas in question to the amount of heat trapped by a similar
mass of carbon
dioxide. GWP is calculated over a specific time interval, such as 20, 100 or
500 years. GWP is
expressed as a factor of carbon dioxide, wherein carbon dioxide has a
standardized GWP of 1.
For example, the 20 year GWP, e., GWP20, of methane is 72. This means that, if
the same mass
of methane and carbon dioxide are introduced into the atmosphere, the methane
will trap 72
times more heat than the carbon dioxide over the next 20 years.
[00381 A "heat exchanger" broadly means any device capable of
transferring heat from one
media to another media, including particularly any structure, e.g., device
commonly referred to
as a heat exchanger. Heat exchangers include "direct heat exchangers" and
"indirect heat
exchangers." Thus, a heat exchanger may be a shell-and-tube, spiral, hairpin,
core, core-and-
kettle, double-pipe, brazed aluminum, spiral wound, or any other type of known
heat exchanger.
"Heat exchanger" may also refer to any column, tower, unit or other
arrangement adapted to
allow the passage of one or more streams there through, and to affect direct
or indirect heat
exchange between one or more lines of refrigerant, and one or more feed
streams.
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[00391 A "hydrocarbon" is an organic compound that primarily includes
the elements
hydrogen and carbon, although nitrogen, sulfur, oxygen, metals, or any number
of other elements
may be present in small amounts. As used herein, hydrocarbons generally refer
to components
found in natural gas, oil, or chemical processing facilities.
100401 "Liquefied natural gas" or "LNG" is natural gas generally known to
include a high
percentage of methane. However, LNG may also include trace amounts of other
compounds.
The other elements or compounds may include, but are not limited to, ethane,
propane, butane,
carbon dioxide, nitrogen, helium, hydrogen sulfide, or combinations thereof,
that have been
processed to remove one or more components (for instance, helium) or
impurities (for instance,
water and/or heavy hydrocarbons) and then condensed into a liquid at almost
atmospheric
pressure by cooling.
10041i "Liquefied petroleum gas" or "LPG" generally refers to a mixture
of propane, butane,
and other light hydrocarbons derived from refining crude oil. At normal
temperature, LPG is a
gas. However, LPG can be cooled or subjected to pressure to facilitate storage
and
transportation.
[00421 The "melting point" or "MP" of a substance is the temperature at
which the solid and
liquid forms of the substance can exist in equilibrium. As heat is applied to
the solid form of a
substance, its temperature will increase until the melting point is reached.
The application of
additional heat will then convert the substance from solid form to liquid form
with no
temperature change. When the entire substance has melted, additional heat will
raise the
temperature of the liquid form of the substance.
100431 "Mixed refrigerant processes" or "MR processes" may include, but
are not limited to,
a "single mixed refrigerant" or "SMR" cycle, a hydrocarbon pre-cooled MR
cycle, a "dual mixed
refrigerant" or "DMR" cycle, and a "triple mixed refrigerant" or "TMR" cycle.
In general, MRs
can include hydrocarbon and/or non-hydrocarbon components. MR processes employ
at least
one mixed component refrigerant, but can additionally employ one or more pure-
component
refrigerants as well.
10044] "Natural gas" refers to a multi-component gas obtained from a
crude oil well or from
a subterranean gas-bearing formation. The composition and pressure of natural
gas can vary
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significantly. A typical natural gas stream contains methane (CH4) as a major
component, i.e.,
greater than 50 mol % of the natural gas stream is methane. The natural gas
stream can also
contain ethane (C2H6), higher molecular weight hydrocarbons (e.g., C3-C20
hydrocarbons), one or
more acid gases (e.g., carbon dioxide or hydrogen sulfide), or any
combinations thereof. The
natural gas can also contain minor amounts of contaminants such as water,
nitrogen, iron sulfide,
wax, crude oil, or any combinations thereof The natural gas stream may be
substantially
purified prior to use in embodiments, so as to remove compounds that may act
as poisons.
100451 As used herein, "natural gas liquids" or "NGLs" refer to mixtures
of hydrocarbons
whose components are, for example, typically heavier than methane and
condensed from a
natural gas. Some examples of hydrocarbon components of NGL streams include
ethane,
propane, butane, and pentane isomers, benzene, toluene, and other aromatic
compounds.
10046] A "nitrogen rejection unit" or "NRU" refers to any system or
device configured to
receive a natural gas feed stream and produce substantially pure products
streams, e.g., a salable
methane stream and a nitrogen stream including about 30% to 99% N2. Examples
of types of
NRU's include cryogenic distillation, pressure swing adsorption (PSA),
membrane separation,
lean oil absorption, and solvent absorption.
10047] The "ozone depletion potential" or "ODP" of a chemical compound
is the relative
amount of degradation to the ozone layer it can cause, where
trichlorofluoromethane, i.e., R-11,
is fixed at an ODP of 1Ø Chlorodifluoromethane, i.e., R-22, for example, has
an ODP of 0.055.
Many HFCs, such as R-32, have ODPs approaching zero.
[00481 A "refrigerant component," in a refrigeration system, will absorb
heat at a lower
temperature and pressure through evaporation and will reject heat at a higher
temperature and
pressure through condensation. Illustrative refrigerant components may
include, but are not
limited to, alkanes, alkenes, and alkynes having one to five carbon atoms,
nitrogen, chlorinated
hydrocarbons, fluorinated hydrocarbons, other halogenated hydrocarbons, noble
gases, and
mixtures or combinations thereof
10049] Refrigerant components often include single component
refrigerants. A single
component refrigerant with a single halogenated hydrocarbon has an associated
"R-" designation
of two or three numbers, which reflects its chemical composition. Adding 90 to
the number
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gives three digits that stand for the number of carbon, hydrogen, and fluorine
atoms,
respectively. The first digit of a refrigerant with three numbers is one unit
lower than the number
of carbon atoms in the molecule. If the molecule contains only one carbon
atom, the first digit is
omitted. The second digit is one unit greater than the number of hydrogen
atoms in the
molecule. The third digit is equal to the number of fluorine atoms in the
molecule. Remaining
bonds not accounted for are occupied by chlorine atoms. A suffix of a lower-
case letter "a," "b,"
or "c" indicates increasingly unsymmetrical isomers. As a special case, the R-
400 series is made
up of zeotropic blends, and the R-500 series is made up of azeotropic blends.
The rightmost
digit is assigned arbitrarily by ASHRAE, an industry organization.
100501 "Substantial" when used in reference to a quantity or amount of a
material, or a
specific characteristic thereof, refers to an amount that is sufficient to
provide an effect that the
material or characteristic was intended to provide. The exact degree of
deviation allowable may
depend, in some cases, on the specific context.
Overview
100.511 Embodiments described herein provide a hydrocarbon processing
system. The
hydrocarbon processing system includes a refrigeration system for producing
LNG from a
natural gas. The refrigeration system includes a fluorocarbon refrigeration
system that utilizes a
mixed fluorocarbon refrigerant to cool the natural gas. The refrigeration
system may also
include a nitrogen refrigeration system and/or a methane autorefrigeration
system, which may be
used to further cool the natural gas to produce LNG. In addition, the
hydrocarbon processing
system may include an NRU, which may be used to remove nitrogen from the
natural gas. In
some embodiments, the nitrogen that is removed from the natural gas via the
NRU is used to
provide additional cooling for the natural gas.
[00521 Hydrocarbon processing systems include any number of systems
known to those
skilled in the art. Hydrocarbon production and treatment processes include,
but are not limited
to, chilling natural gas for NGL extraction, chilling natural gas for
hydrocarbon dew point
control, chilling natural gas for CO2 removal, LPG production storage,
condensation of reflux in
deethanizers or demethanizers, and natural gas liquefaction to produce LNG.
[00531 Although many refrigeration cycles have been used to process
hydrocarbons, one
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cycle that is used in LNG liquefaction plants is the cascade cycle, which uses
multiple single
component refrigerants in heat exchangers arranged progressively to reduce the
temperature of
the gas to a liquefaction temperature. Another cycle that is used in LNG
liquefactions plants is
the multi-component refrigeration cycle, which uses a multi-component
refrigerant in specially
designed exchangers. In addition, another cycle that is used in LNG
liquefaction plants is the
expander cycle, which expands gas from feed gas pressure to a low pressure
with a
corresponding reduction in temperature. Natural gas liquefaction cycles may
also use variations
or combinations of these three cycles.
100.541 LNG is prepared from a feed gas by refrigeration and liquefaction
technologies.
Optional steps include condensate removal, CO2 removal, dehydration, mercury
removal,
nitrogen stripping, H2S removal, and the like. After liquefaction, LNG may be
stored or loaded
on a tanker for sale or transport. Conventional liquefaction processes can
include: APCI Propane
pre-cooled mixed refrigerant; C3MR; DUAL MR; Phillips Optimized Cascade; Prico
SMR;
TEAL dual pressure mixed refrigerant; Linde/Statoil multi fluid cascade; Axens
DMR;
ExxonMobil's Enhanced Mixed Refrigerant (EMR); and the Shell processes C3MR
and DMR.
[00551 Carbon dioxide removal, i.e., separation of methane and lighter
gases from CO2 and
heavier gases, may be achieved with cryogenic distillation processes, such as
the Controlled
Freeze Zone technology available from ExxonMobil Corporation.
100.561 While the method and systems described herein are discussed with
respect to the
formation of LNG from natural gas, the method and systems may also be used for
a variety of
other purposes. For example, the method and systems described herein may be
used to chill
natural gas for hydrocarbon dew point control, perform natural gas liquid
(NGL) extraction,
separate methane and lighter gases from CO2 and heavier gases, prepare
hydrocarbons for LPG
production, or condense a reflux stream in deethanizers and/or demethanizers,
among others.
Refrigerants
[00571 The refrigerants that are utilized according to embodiments
described herein may be
mixed refrigerants, where each mixed refrigerant may include two or more
single component
and/or multicomponent refrigerants. Refrigerants may be imported and stored on-
site or,
alternatively, some of the components of the refrigerant may be prepared on-
site, typically by a
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distillation process integrated with the hydrocarbon processing system. In
various embodiments,
the mixed refrigerants that are utilized according to embodiments described
herein include
fluorocarbons (FCs), such as HFCs. Exemplary refrigerants are commercially
available from
DuPont Corporation, including the ISCEONO family of refrigerants, the SUVA
family of
refrigerants, the OPTEONO family of refrigerants, and the FREON family of
refrigerants.
[00581 Multicomponent refrigerants are commercially available. For
example, R-401A is a
HCFC blend of R-32, R-152a, and R-124. R-404A is a HFC blend of 52 wt.% R-
143a, 44 wt.%
R-125, and 4 wt.% R-134a. R-406A is a blend of 55 wt.% R-22, 4 wt.% R-600a,
and 41 wt.% R-
142b. R-407A is a HFC blend of 20 wt.% R-32, 40 wt.% R-125, and 40 wt.% R-
134a. R-407C
is a hydrofluorocarbon blend of R-32, R-125, and R-134a. R-408A is a HCFC
blend of R-22, R-
125, and R-143a. R-409A is a HCFC blend of R-22, R-124, and R-142b. R-410A is
a blend of
R-32 and R-125. R-500 is a blend of 73.8 wt.% R-12 and 26.2 wt.% of R-152a. R-
502 is a
blend of R-22 and R-115. R-508B is a blend of R-23 and R-116. More specific
information
regarding particular refrigerants that may be used according to embodiments
described herein is
shown below in Table 1.
[00591 The ozone depletion potentials for all the refrigerants shown in
Table 1 are equal to
zero. The "Safety Group" shown in Table 1 is an ASHRAE designation. A
designation of "A"
indicates that the Occupational Exposure Limit (OEL) for the refrigerant is
above 400 parts per
million (ppm). A designation of "B" indicates that the OEL for the refrigerant
is below 400
ppm. A number of "1" indicates that the refrigerant is non-flammable. A number
of "2"
indicates that the refrigerant is slightly flammable, and a number of "3"
indicates that the
refrigerant is highly flammable. An "L" suffix indicates that the refrigerant
has a very low flame
propagation speed.
100601 It is to be understood that the embodiments described herein are
not limited to the use
of the refrigerants listed in Table 1. Rather, any other suitable types of non-
flammable
refrigerants, or mixtures thereof, may also be used according to embodiments
described herein.
For example, any suitable types of HFCs, HF0s, and/or inert compounds can be
combined to
form a mixed refrigerant according to embodiments described herein.
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TABLE 1: Refrigerants
Atm.
ASHRAE NBP MP Safety Life
Number Chemical Name Formula MW C C Group
years GWP too
R-50 Methane CH4 16 -162 -182 A3 12
25
R-14 Tetrafluoro methane CF4 88 -128 -183 Al
50,000 7,390
R-23 Trifluoro methane CHF3 70 -82 -155 Al 270
14,800
R-41 Fluor methane CH3F 34 -78 -142 A3 2.4
92
R-32 Difluoro methane CH2F2 52 -52 -136 A2L 4.9
675
R-218 Octafluoro propane C3 F8 188 -37 -148 Al
2,600 8,830
R-227ea 1,1,1,2,3,3,3-heptafluoro propane CF3CFHCF3 170 -16
-131 Al 34.2 3,220
R-245fa 1,1,1,3,3-pentafluoro propane CF3CH2CHF2 134 15 -
102 B1 7.6 1,030
R-116 Hexafluoro ethane C2F6 138 -78 -101 Al
10,000 12,200
R-125 1,1,1,2,2 Pentafluoro ethane C2HF5 120 -49 -103
Al 29 3,500
R-143a 1,1,1-trifluoro ethane CH3CF3 84 -48 -111
A2L 52 4,470
R-1234yf 2,3,3,3-Tetrafluoropropene C3H2F4 114 -29 -152
A2L 0.03 o
R-134a 1,1,1,2-tetrafluoro ethane CH2FCF3 102 -26 -103
Al 14 1,430
R-152a Eldifluoro ethane CH2CHF2 66 -25 -117 A2 1.4
124
R-1234ze 1,3,3,3-Tetrafluoropropene C3H2F4 114 -19 A2L
.. o
R-C318 Octafluoro cyclobutane (-CF2-)4 200 -6 -40
Al 3,200 10,300
R-236fa 1,1,1,3,3,3-hexafluoro propane CF3CH2CF3 152 -2 -96
Al 240 9,810
R-245ca 1,1,2,2,3-pentafluoro propane CHF2CF2CH2F 134 25 -
82 B1 6.2 693
HFE-347mcc Heptafluoropropyl, methyl ether C3 F7OCH3 200 34 -
123 ¨ 4.9 o
R-728 Nitrogen (non-HFC) N2 28 -196 -210 Al .0
o
R-740 Argon (non-HFC) AT 40 -186 -189 Al .0
o
R-784 Krypton (non-HFC) Kr
Xenon (non-HFC) Xe
R-744 Carbon dioxide (non-HFC) CO2 44 -57 -78 Al
33,000 1
[00611 According to embodiments described herein, the particular
selection of fluorocarbons
for a mixed refrigerant depends on the desired refrigeration temperatures.
Natural gas liquefies
to form LNG at -162 C. Therefore, in order to produce LNG, a mixed
refrigerant that is capable
of chilling natural gas below -162 C may be selected. In some cases,
refrigerants may be used
at warmer temperatures, and another refrigeration process, such as an
autorefrigeration process,
may be used to aid in the production of LNG.
[00621 When selecting a set of fluorocarbons for a mixed refrigerant,
the normal boiling
point and the melting point may both be taken into consideration. It may be
desirable for the
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temperature of the mixed refrigerant to be above its freezing point during the
entire refrigeration
cycle, so that the refrigerant will not form solids and cause plugging in the
system. In addition, it
may be desirable to be above atmospheric pressure during the entire
refrigeration cycle to avoid
air contamination of the mixed refrigerant. In various embodiments, the
components of the
mixed refrigerant are selected such that the melting point of each component
is below the
chilling temperature. There may be some degree of flexibility in the melting
point of the
components, since a mixture does not start to freeze at the warmest pure
component melting
point. Some melting point depression occurs when a high melting point
component is diluted in
other, non-freezing components and approaches the eutectic point. For example,
R-245fa, which
has a melting point of -102 C, can be used at lower temperatures if it is at
a sufficiently low
concentration in the mixed refrigerant.
[00631 The particular selection of fluorocarbons for a mixed refrigerant
may also depend on
the specific type of refrigeration system for which the mixed refrigerant is
to be used. For
example, SMR cycles may use mixed refrigerants including a mixture of R-14, R-
23, R-32, R-
227ea, R-245fa, or the like. Other possible refrigerant components for the
mixed refrigerant
include R-41, R-218, R-1234yf, R-1234ze, R-152a, and the like. In general, the
components of a
mixed refrigerant may be selected such that their NBPs evenly cover the
desired refrigeration
range.
100641 In various embodiments, any of a number of different types of
hydrocarbon
processing systems can be used with any of the refrigeration systems described
herein. In
addition, the refrigeration systems described herein may utilize any mixture
of the refrigerants
described herein.
Refrigeration Systems
[00651 Hydrocarbon systems and methods often include refrigeration
systems that utilize
mechanical refrigeration, valve expansion, turbine expansion, or the like.
Mechanical
refrigeration typically includes compression systems and absorption systems,
such as ammonia
absorption systems. Compression systems are used in the gas processing
industry for a variety of
processes. For example, compression systems may be used for chilling natural
gas for NGL
extraction, chilling natural gas for hydrocarbon dew point control, LPG
production storage,
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condensation of reflux in deethanizers or demethanizers, natural gas
liquefaction to produce
LNG, or the like.
[00661 Fig. 1 is a process flow diagram of a single stage refrigeration
system 100. In various
embodiments, the single stage refrigeration system 100 uses a mixed
fluorocarbon refrigerant.
The use of a mixed fluorocarbon refrigerant may allow the single stage
refrigeration system 100
to maintain high efficiency over a wide range of temperatures. Further, in
various embodiments,
the single stage refrigeration system 100 is implemented upstream of a
nitrogen refrigeration
system or methane autorefrigeration system including an NRU. Multiple single
stage
refrigeration systems 100 may also be implemented in series upstream of such a
nitrogen
refrigeration system or methane autorefrigeration system.
[00671 The single stage refrigeration system 100 includes an expansion
device 102, a chiller
104, a compressor 106, a condenser 108, and an accumulator 110. The expansion
device 102
may be an expansion valve or a hydraulic expander, for example. A saturated
liquid refrigerant
112 may flow from the accumulator 110 to the expansion device 102, and may
expand across the
expansion device 102 isenthalpically. On expansion, some vaporization occurs,
creating a
chilled refrigerant mixture 114 that includes both vapor and liquid. The
refrigerant mixture 114
may enter the chiller 104, also known as the evaporator, at a temperature
lower than the
temperature to which a process stream 116, such as a natural gas, is to be
cooled. The process
stream 116 flows through the chiller 104 and exchanges heat with the
refrigerant mixture 114.
As the process stream 116 exchanges heat with the refrigerant mixture 114, the
process stream
116 is cooled, while the refrigerant mixture 114 vaporizes, creating a
saturated vapor refrigerant
118.
[00681 After leaving the chiller 104, the saturated vapor refrigerant
118 is compressed within
the compressor 106, and is then flowed into the condenser 108. Within the
condenser 108, the
saturated vapor refrigerant 118 is converted to a saturated, or slightly sub-
cooled, liquid
refrigerant 120. The liquid refrigerant 120 may then be flowed from the
condenser 108 to the
accumulator 110. The accumulator 110, which is also known as a surge tank or
receiver, may
serve as a reservoir for the liquid refrigerant 120. The liquid refrigerant
120 may be stored
within the accumulator 110 before being expanded across the expansion device
102 as the
saturated liquid refrigerant 112.
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[00691 It is to be understood that the process flow diagram of Fig. 1 is
not intended to
indicate that the single stage refrigeration system 100 is to include all the
components shown in
Fig. 1. Further, the single stage refrigeration system 100 may include any
number of additional
components not shown in Fig. 1, depending on the details of the specific
implementation. For
example, in some embodiments, a refrigeration system can include two or more
compression
stages. In addition, the refrigeration system 100 may include an economizer,
as discussed further
with respect to Fig. 2.
f00701 Fig. 2 is a process flow diagram of a two stage refrigeration
system 200 including an
economizer 202. Like numbered items are as described with respect to Fig. 1.
In various
embodiments, the two stage refrigeration system 200 utilizes a fluorocarbon
refrigerant, such as
an azeotrope (R-5XX) or a near-azeotrope (R-4XX). Further, in various
embodiments, the two
stage refrigeration system 200 is implemented upstream of a nitrogen
refrigeration system or
methane autorefrigeration system including an NRU. Multiple two stage
refrigeration systems
200 may also be implemented in series upstream of such a nitrogen
refrigeration system or
methane autorefrigeration system.
[00711 The economizer 202 may be any device or process modification that
decreases the
compressor power usage for a given chiller duty. Conventional economizers 202
include, for
example, flash tanks and heat exchange economizers. Heat exchange economizers
utilize a
number of heat exchangers to transfer heat between process streams. This may
reduce the
amount of energy input into the two stage refrigeration system 200 by heat
integrating process
streams with each other.
[0072] As shown in Fig. 2, the saturated liquid refrigerant 112 leaving
the accumulator 110
may be expanded across the expansion device 102 to an intermediate pressure at
which vapor
and liquid may be separated. For example, as the saturated liquid refrigerant
112 flashes across
the expansion device 102, a vapor refrigerant 204 and a liquid refrigerant 206
are produced at a
lower pressure and temperature than the saturated liquid refrigerant 112. The
vapor refrigerant
204 and the liquid refrigerant 206 may then be flowed into the economizer 202.
In various
embodiments, the economizer 202 is a flash tank that effects the separation of
the vapor
refrigerant 204 and the liquid refrigerant 206. The vapor refrigerant 204 may
be flowed to an
intermediate pressure compressor stage, at which the vapor refrigerant 204 may
be combined
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with saturated vapor refrigerant 118 exiting a first compressor 210, creating
a mixed saturated
vapor refrigerant 208. The mixed saturated vapor refrigerant 208 may then be
flowed into a
second compressor 212.
[00731 From the economizer 202, the liquid refrigerant 206 may be
isenthalpically expanded
across a second expansion device 214. The second expansion device 214 may be
an expansion
valve or a hydraulic expander, for example. On expansion, some vaporization
may occur,
creating a refrigerant mixture 216 that includes both vapor and liquid,
lowering the temperature
and pressure. The refrigerant mixture 216 will have a higher liquid content
than refrigerant
mixtures in systems without economizers. The higher liquid content may reduce
the refrigerant
circulation rate and/or reduce the power usage of the first compressor 210.
[00741 The refrigerant mixture 216 enters the chiller 104, also known as
the evaporator, at a
temperature lower than the temperature to which the process stream 116 is to
be cooled. The
process stream 116 is cooled within the chiller 104, as discussed with respect
to Fig. 1. In
addition, the saturated vapor refrigerant 118 is flowed through the
compressors 210 and 212 and
the condenser 108, and the resulting liquid refrigerant 120 is stored within
the accumulator 110,
as discussed with respect to Fig. 1.
100751 It is to be understood that the process flow diagram of Fig. 2 is
not intended to
indicate that the two stage refrigeration system 200 is to include all the
components shown in
Fig. 2. Further, the two stage refrigeration system 200 may include any number
of additional
components not shown in Fig. 2, depending on the details of the specific
implementation. For
example, the two stage refrigeration system 200 may include any number of
additional
economizers or other types of equipment not shown in Fig. 2. In addition, the
economizer 202
may be a heat exchange economizer rather than a flash tank. The heat exchange
economizer
may also be used to decrease refrigeration circulation rate and reduce
compressor power usage.
100761 In some embodiments, the two stage refrigeration system 200 includes
more than one
economizer 202, as well as more than two compressors 210 and 212. For example,
the two stage
refrigeration system 200 may include two economizers and three compressors. In
general, if the
refrigeration system 200 includes X number of economizers, the refrigeration
system 200 will
include X +1 number of compressors. Such a refrigeration system 200 with
multiple
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economizers may form part of a cascade refrigeration system.
100771 Fig. 3 is a process flow diagram of a single stage refrigeration
system 300 including a
heat exchanger economizer 302. Like numbered items are as described with
respect to Fig. 1. In
various embodiments, the single stage refrigeration system 300 utilizes a
mixed fluorocarbon
refrigerant. Further, in various embodiments, the single stage refrigeration
system 300 is
implemented upstream of a nitrogen refrigeration system or methane
autorefrigeration system
including an NRU. Multiple single stage refrigeration systems 300 may also be
implemented in
series upstream of such a nitrogen refrigeration system or methane
autorefrigeration system.
[00781 As shown in Fig. 3, the saturated liquid refrigerant 112 leaving
the accumulator 110
may be expanded across the expansion device 102 to an intermediate pressure at
which vapor
and liquid may be separated, producing the refrigerant mixture 114. The
refrigerant mixture 114
may be flowed into the chiller 104 at a temperature lower than the temperature
to which the
process stream 116 is to be cooled. The process stream 116 may be cooled
within the chiller
104, as discussed with respect to Fig. 1.
100791 From the chiller 104, the saturated vapor refrigerant 118 may be
flowed through the
heat exchanger economizer 302. The cold, low-pressure saturated vapor
refrigerant 118 may be
used to subcool the saturated liquid refrigerant 112 within the heat exchanger
economizer 302.
The superheated vapor refrigerant 304 exiting the heat exchanger economizer
302 may then be
flowed through the compressor 106 and the condenser 108, and the resulting
liquid refrigerant
120 may be stored within the accumulator 110, as discussed with respect to
Fig. 1.
[00801 It is to be understood that the process flow diagram of Fig. 3 is
not intended to
indicate that the single stage refrigeration system 300 is to include all the
components shown in
Fig. 3. Further, the single stage refrigeration system 300 may include any
number of additional
components not shown in Fig. 3, depending on the details of the specific
implementation.
100811 Fig. 4 is a process flow diagram of an LNG production system 400. As
shown in Fig.
4, LNG 402 may be produced from a natural gas stream 404 using a number of
different
refrigeration systems. As shown in Fig. 4, a portion of the natural gas stream
404 may be
separated from the natural gas stream 404 prior to entry into the LNG
production system 400,
and may be used as a fuel gas stream 406. The remaining natural gas stream 404
may be flowed
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into an initial natural gas processing system 408. Within the natural gas
processing system 408,
the natural gas stream 404 may be purified and cooled. For example, the
natural gas stream 404
may be cooled using a first mixed fluorocarbon refrigerant 410, a second mixed
fluorocarbon
refrigerant 412, and a high-pressure nitrogen refrigerant 414. The cooling of
the natural gas
stream 404 may result in the production of the LNG 402. In some embodiments,
the broader
temperature range of a mixed refrigerant system will make it possible to use a
single mixed
refrigerant for both the first mixed fluorocarbon refrigerant 410 and the
second mixed
fluorocarbon refrigerant 412.
100821 Within the LNG production system 400, heavy hydrocarbons 416 may
be removed
from the natural gas stream 406, and a portion of the heavy hydrocarbons 416
may be used to
produce gasoline 418 within a heavy hydrocarbon processing system 420. In
addition, any
residual natural gas 422 that is separated from the heavy hydrocarbons 416
during the production
of the gasoline 418 may be returned to the natural gas stream 404.
100831 The produced LNG 402 may include some amount of nitrogen 424.
Therefore, the
LNG 402 may be flowed through an NRU 426. The NRU 426 separates the nitrogen
424 from
the LNG 402, producing the final LNG product.
10084] It is to be understood that the process flow diagram of Fig. 4 is
not intended to
indicate that the LNG production system 400 is to include all the components
shown in Fig. 4.
Further, the LNG production system 400 may include any number of additional
components not
shown in Fig. 4 or different locations for the fluorocarbon refrigerant
chillers within the process,
depending on the details of the specific implementation. For example, any
number of alternative
refrigeration systems may also be used to produce the LNG 402 from the natural
gas stream 404.
In addition, any number of different refrigeration systems may be used in
combination to
produce the LNG 402.
Hydrocarbon Processing Systems for the Production of LNG
[00851 According to embodiments described herein, LNG may be produced
within a
hydrocarbon processing system using mixed fluorocarbon refrigerants. In some
embodiments,
the fluorocarbon components within the mixed fluorocarbon refrigerants are non-
flammable,
non-toxic, and non-reactive. The fluorocarbon components for a particular
mixed fluorocarbon
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refrigerant may be selected such that the cooling curve of the mixed
fluorocarbon refrigerant
closely matches the cooling curve of the LNG being chilled. Matching the
cooling curve of the
mixed fluorocarbon refrigerant to the cooling curve of the LNG may increase
the performance
and efficiency of the hydrocarbon processing system.
100861 Fig. 5 is a process flow diagram of a hydrocarbon processing system
500 including an
SMR cycle 502. The SMR cycle 502 may cool a feed gas 504 to produce LNG 506
using a
mixed fluorocarbon refrigerant 508. The hydrocarbon processing system 500 also
includes a low
pressure NRU 510, which may be used to purify the LNG 506 by separating the
LNG 506 from a
fuel stream 512 including nitrogen.
100871 The SMR cycle 502 includes a heat exchanger 514, a compressor 516, a
condenser
518, and an expansion device 520. The expansion device 520 may be an expansion
valve or a
hydraulic expander, for example. The mixed fluorocarbon refrigerant 508 is
flowed from the
condenser 518 to the heat exchanger 514. Within the heat exchanger 514, the
mixed
fluorocarbon refrigerant 508 cools the feed gas 504 to produce the LNG 506 via
indirect heat
exchange.
[00881 From the heat exchanger 514, the mixed fluorocarbon refrigerant
508 is flowed to the
expansion device 520, and is expanded across the expansion device 520
isenthalpically. On
expansion, some vaporization occurs, creating a chilled mixed fluorocarbon
refrigerant 522 that
includes both vapor and liquid. The chilled mixed fluorocarbon refrigerant 522
is flowed back to
the heat exchanger 514 and is used to aid in the cooling of the feed gas 508
within the heat
exchanger 514. As the feed gas 508 exchanges heat with the chilled mixed
fluorocarbon
refrigerant 522, the chilled mixed fluorocarbon refrigerant 522 vaporizes,
creating a vapor mixed
fluorocarbon refrigerant 524.
[00891 The vapor mixed fluorocarbon refrigerant 524 is then compressed
within the
compressor 516 and flowed into the condenser 518. Within the condenser 518,
the vapor mixed
fluorocarbon refrigerant 524 is converted to a saturated, or slightly sub-
cooled, liquid mixed
fluorocarbon refrigerant 508. The liquid mixed fluorocarbon refrigerant 508 is
then flowed back
into the heat exchanger 514.
[00901 In various embodiments, the LNG 506 that is produced via the SMR
cycle 502
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includes some amount of impurities, such as nitrogen. Therefore, the LNG 506
is flowed to into
the NRU 510. The NRU 510 separates the fuel stream 512 including the nitrogen
from the LNG
506, producing the final LNG product. The final LNG product may then be flowed
from the
hydrocarbon processing system 500 to a desired destination using a pump 526.
100911 It is to be understood that the process flow diagram of Fig. 5 is
not intended to
indicate that the hydrocarbon processing system 500 is to include all the
components shown in
Fig. 5. Further, the hydrocarbon processing system 500 may include any number
of additional
components not shown in Fig. 5, depending on the details of the specific
implementation.
[00921 Fig. 6 is a process flow diagram of the hydrocarbon processing
system 500 of Fig. 5
with the addition of a nitrogen refrigeration system 600. Like numbered items
are as described
with respect to Fig. 5. According to the embodiment shown in Fig. 6, the SMR
cycle 502 may
be operated at a higher temperature. Therefore, the output of the SMR cycle
502 may be cooled
feed gas 504, rather than LNG 506, or may be a mixture of cooled feed gas 504
and LNG 506.
[00931 From the SMR cycle 502, the feed gas 504 is flowed into the
nitrogen refrigeration
system 600. Within the nitrogen refrigeration system 600, the feed gas may be
cooled to produce
the LNG 506 via indirect heat exchange with a nitrogen refrigerant 602 within
a first heat
exchanger 604. The LNG 506 is then flowed into the NRU 510, as discussed with
respect to Fig.
5.
[00941 The nitrogen refrigeration system 600 includes the first heat
exchanger 604, a second
heat exchanger 606, a compressor 608, a condenser 610, and an expander 612.
From the first
heat exchanger 604, the nitrogen refrigerant 602 is flowed through the second
heat exchanger
606. Within the second heat exchanger 606, the nitrogen refrigerant 602 is
cooled via indirect
heat exchange with a chilled, vapor nitrogen refrigerant 614. The nitrogen
refrigerant 602 is then
compressed within the compressor 608 and flowed into the condenser 610.
100951 Within the condenser 610, the nitrogen refrigerant 602 is converted
to the vapor
nitrogen refrigerant 614. The vapor nitrogen refrigerant 614 is flowed through
the second heat
exchanger 606, in which the vapor nitrogen refrigerant 614 exchanges heat with
the warmer
nitrogen refrigerant 602 exiting the first heat exchanger 604.
[00961 The chilled, vapor nitrogen refrigerant 614 is then flowed
through the expander 612.
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The expander 612 expands the vapor nitrogen refrigerant 614 to a low pressure
with a
corresponding reduction in temperature. The resulting cold nitrogen
refrigerant 602 is flowed
through the first heat exchanger 604 to exchange heat with the feed gas 504.
[0097] It is to be understood that the process flow diagram of Fig. 6 is
not intended to
indicate that the hydrocarbon processing system 600 is to include all the
components shown in
Fig. 6. Further, the hydrocarbon processing system 600 may include any number
of additional
components not shown in Fig. 6, depending on the details of the specific
implementation.
[0098] Fig. 7 is a process flow diagram of the hydrocarbon processing
system 500 of Fig. 5
with the addition of a methane autorefrigeration system 700. Like numbered
items are as
described with respect to Fig. 5. According to the embodiment shown in Fig. 7,
the SMR cycle
502 may be operated at a higher temperature. Therefore, the output of the SMR
cycle 502 may
be cooled feed gas 504, rather than LNG 506, or may be a mixture of cooled
feed gas 504 and
LNG 506.
[0099] From the SMR cycle 502, the cooled feed gas 504 is flowed into
the NRU 510. The
NRU 510 purifies the feed gas 504, producing an LNG bottoms stream 702 and a
fuel gas
overhead stream 704. The LNG bottoms stream 702 is flowed through an expansion
device 706,
such as an expansion valve or hydraulic expander, and into a heat exchanger
708. Within the
heat exchanger 708, the LNG bottoms stream 702 exchanges heat with the
overhead fuel stream
704, cooling the overhead fuel stream 704 and producing a mixed fuel stream
710 including both
the vapor fuel stream 512 and a liquid fuel stream 712.
[0100] The mixed fuel stream 710 is then flowed into a flash drum 714.
The flash drum 714
separates the vapor fuel stream 512 from the liquid fuel stream 712. The
liquid fuel stream 712
may then be flowed back into the NRU 510 as reflux.
[0101] As the LNG bottoms stream 702 exchanges heat with the overhead
fuel stream 704
within the heat exchanger 708, it may be partially vaporized, producing a
mixed phase feed
stream 716. From the heat exchanger 708, the mixed phase feed stream 716 is
flowed into a first
flash drum 718 within the methane autorefrigeration system 700.
[0102] The first flash drum 718 separates the mixed phase feed stream
716 into a vapor
stream 720 that includes primarily natural gas and an LNG stream 722. The
vapor stream 720 is
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flowed into a first compressor 724. From the first compressor 724, the
resulting natural gas
stream 726 may be combined with the initial feed gas 504 prior to entry of the
feed gas 504 into
the SMR cycle 502.
[0103] From the first flash drum 718, the LNG stream 722 is flowed
through an expansion
device 728, such as an expansion valve or hydraulic expander, which may
control the flow of the
LNG stream 728 into a second flash drum 730. Specifically, the expansion
device 728 may
allow a portion of the liquid from the LNG stream 722 to flash, creating a
mixed phase stream
that is flowed into the second flash drum 730.
[0104] The second flash drum 730 separates the mixed phase stream into
the final LNG
product 506 and a vapor stream 732 that includes primarily natural gas. The
vapor stream 732 is
flowed into a second compressor 734. From the second compressor 734, the vapor
stream 732 is
combined with the vapor stream 720 from the first flash drum 718 prior to
entry of the vapor
stream 720 into the first compressor 724. Furthermore, from the second flash
drum 730, the final
LNG product 506 may be flowed to a desired destination using the pump 526.
[0105] It is to be understood that the process flow diagram of Fig. 7 is
not intended to
indicate that the hydrocarbon processing system 700 is to include all the
components shown in
Fig. 7. Further, the hydrocarbon processing system 700 may include any number
of additional
components not shown in Fig. 7, depending on the details of the specific
implementation.
[0106] Fig. 8 is a process flow diagram of a hydrocarbon processing
system 800 including a
pre-cooled SMR cycle 802. The pre-cooled SMR cycle 802 may cool a feed gas 804
to produce
LNG 806 using a mixed fluorocarbon refrigerant 808. The hydrocarbon processing
system 800
also includes a low pressure NRU 810, which may be used to purify the LNG 806
by separating
the LNG 806 from a fuel stream 812 including nitrogen.
[0107] Within the pre-cooled SMR cycle 802, the incoming feed gas 804 is
pre-cooled and
partially condensed in a first chiller 814 via indirect heat exchange with a
fluorocarbon
refrigerant. For example, the feed gas 804 may be cooled in the first chiller
814 using a
refrigerant blend such as R-410a or R-404a, or using a pure component
refrigerant such as R-
125, R-32, or R-218.
[0108] The chilled feed gas 816 is then flowed into a main cryogenic
heat exchanger 818.
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Within the main cryogenic heat exchanger 818, the feed gas 816 is cooled to
produce the LNG
806 via indirect heat exchange with the mixed fluorocarbon refrigerant 808.
The main cryogenic
heat exchanger 818 may include a number of small-diameter, spiral-wound tube
bundles 820,
which may permit very close temperature matches between the chilled feed gas
816 and the
mixed fluorocarbon refrigerant 808.
[0109] After the mixed fluorocarbon refrigerant 808 flows through the
main cryogenic heat
exchanger 818, the mixed fluorocarbon refrigerant 808 is expanded across an
expansion device
822, such as an expansion valve or hydraulic expander. On expansion, some
vaporization
occurs, creating a chilled mixed fluorocarbon refrigerant 824 that includes
both vapor and liquid.
The chilled mixed fluorocarbon refrigerant 824 is then sprayed into the main
cryogenic heat
exchanger 818 via a number of spray nozzles 826. In various embodiments,
spraying the chilled
mixed fluorocarbon refrigerant 824 into the main cryogenic heat exchanger 818
provides for
additional cooling of the feed gas 816 and the mixed fluorocarbon refrigerant
808 flowing
through the tube bundles 820.
[0110] The chilled mixed fluorocarbon refrigerant 824 is then flowed out of
the main
cryogenic heat exchanger 818 as a bottoms stream 828. The bottoms stream 828
is compressed
in a compressor 830, producing a compressed mixed fluorocarbon refrigerant
832. The
compressed mixed fluorocarbon refrigerant 832 is chilled and partially
condensed within a
second chiller 834 and a third chiller 836. The resulting chilled mixed
fluorocarbon refrigerant
838 is flowed into a flash drum 839, which separates the chilled mixed
fluorocarbon refrigerant
838 into a vapor stream and a liquid stream. The vapor stream is flowed into
the main cryogenic
heat exchanger 818 as the mixed fluorocarbon refrigerant 808, and the liquid
stream is flowed
into the main cryogenic heat exchanger 818 as an additional mixed fluorocarbon
refrigerant 840.
The additional mixed fluorocarbon refrigerant 840 may provide cooling for the
mixed
fluorocarbon refrigerant 808 via indirect heat exchange with the mixed
fluorocarbon refrigerant
808.
[0111] Upon exiting the main cryogenic heat exchanger 818, the
additional mixed
fluorocarbon refrigerant 840 is expanded across an expansion device 842, such
as an expansion
valve or hydraulic expander. On expansion, some vaporization occurs, creating
a chilled mixed
fluorocarbon refrigerant 844 that includes both vapor and liquid. The chilled
mixed fluorocarbon
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refrigerant 844 is then sprayed into the main cryogenic heat exchanger 818 via
a number of
additional spray nozzles 846. After flowing through the main cryogenic heat
exchanger 818, the
chilled mixed fluorocarbon refrigerant 844 is flowed out of the main cryogenic
heat exchanger
818 along with the bottoms stream 828.
[0112] From the main cryogenic heat exchanger 818, the produced LNG 806 is
flowed
through an expansion device 848, such as an expansion valve or hydraulic
expander, and into the
NRU 810. The NRU 810 separates the fuel stream 812 from the LNG 806, producing
the final
LNG product. The final LNG product may then be flowed from the hydrocarbon
processing
system 800 to a desired destination using a pump 850.
[0113] It is to be understood that the process flow diagram of Fig. 8 is
not intended to
indicate that the hydrocarbon processing system 800 is to include all the
components shown in
Fig. 8. Further, the hydrocarbon processing system 800 may include any number
of additional
components not shown in Fig. 8, depending on the details of the specific
implementation. In
some embodiments, the mixed fluorocarbon refrigerant 808 used in the main
cryogenic heat
exchanger 818 of Fig. 8 includes nitrogen, e.g., R-728, and/or argon, e.g., R-
740, in addition to
one or more fluorocarbon refrigerant components.
[0114] Fig. 9 is a process flow diagram of a hydrocarbon processing
system 900 including a
DMR cycle 902. The DMR cycle 902 may include a warm MR cycle and a cold MR
cycle
connected in series. The DMR cycle 902 may be used to cool a feed gas 904 to
produce LNG
906 using a first mixed fluorocarbon refrigerant 908 within the warm MR cycle
and a second
mixed fluorocarbon refrigerant 910 within the cold MR cycle. The hydrocarbon
processing
system 900 also includes a low pressure NRU 912, which may be used to purify
the LNG 906 by
separating the LNG 906 from a fuel stream 914 including nitrogen.
[0115] In some embodiments, the first mixed fluorocarbon refrigerant 908
within the warm
MR cycle includes R-32, R-152a, R-245fa, R-227ea, HFE-347mcc, and/or other
high boiling
components. In addition, in some embodiments, the second mixed fluorocarbon
refrigerant 910
within the cold MR cycle includes R-14, R-170, R-41, xenon, R-23, R-116, R-
1150, R-50, R-
784, and/or other low boiling components.
[0116] Within the hydrocarbon processing system 900, the feed gas 904 is
cooled to produce
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the LNG 906 using a first heat exchanger 916 and a second heat exchanger 918.
The feed gas
904 is cooled within the first heat exchanger 916 via indirect heat exchange
along with the first
mixed fluorocarbon refrigerant 908 and the second mixed fluorocarbon
refrigerant 910.
[0117] From the first heat exchanger 916, the first mixed fluorocarbon
refrigerant 908 is
flowed to an expansion device 920, such as an expansion valve or hydraulic
expander, and is
expanded across the expansion device 920 isenthalpically. On expansion, some
vaporization
occurs, creating a chilled mixed fluorocarbon refrigerant 922 that includes
both vapor and liquid.
The chilled mixed fluorocarbon refrigerant 922 is flowed back to the first
heat exchanger 916
and is used to cool the first mixed fluorocarbon refrigerant 908, the second
mixed fluorocarbon
refrigerant 910, and the feed gas 904 within the first heat exchanger 916. As
the first mixed
fluorocarbon refrigerant 908, the second mixed fluorocarbon refrigerant 910,
and the feed gas
904 exchange heat with the chilled mixed fluorocarbon refrigerant 922, the
chilled mixed
fluorocarbon refrigerant 922 vaporizes, creating a vapor mixed fluorocarbon
refrigerant 924.
[0118] The vapor mixed fluorocarbon refrigerant 924 is then compressed
within a
compressor 926 and condensed within a condenser 928. The condensed mixed
fluorocarbon
refrigerant is then flowed back into the first heat exchanger 916 as the first
mixed fluorocarbon
refrigerant 908.
[0119] From the first heat exchanger 916, the second mixed fluorocarbon
refrigerant 910 is
flowed into the second heat exchanger 918. Within the second heat exchanger
918, the second
mixed fluorocarbon refrigerant 910 is further cooled along with the feed gas
904, producing the
LNG 906.
[0120] Upon exiting the second heat exchanger 918, the second mixed
fluorocarbon
refrigerant 910 is flowed to an expansion device 930, such as an expansion
valve or hydraulic
expander, and is expanded across the expansion device 930 isenthalpically. On
expansion, some
vaporization occurs, creating a chilled mixed fluorocarbon refrigerant 932
that includes both
vapor and liquid. The chilled mixed fluorocarbon refrigerant 932 is flowed
back to the second
heat exchanger 918 and is used to cool both the feed gas 904 and the second
mixed fluorocarbon
refrigerant 910 within the second heat exchanger 918. As the feed gas 904
exchanges heat with
the chilled mixed fluorocarbon refrigerant 932, the chilled mixed fluorocarbon
refrigerant 932
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vaporizes, creating a vapor mixed fluorocarbon refrigerant 934.
[0121] The vapor mixed fluorocarbon refrigerant 934 is then compressed
within a
compressor 936, and cooled within a heat exchanger 938. The condensed mixed
fluorocarbon
refrigerant is flowed back into the first heat exchanger 916 as the second
mixed fluorocarbon
refrigerant 910.
[0122] In various embodiments, the LNG 906 that is produced via the DMR
cycle 902
includes some amount of impurities, such as nitrogen. Therefore, the LNG 906
is flowed to into
the NRU 912. The NRU 912 separates the fuel stream 914 from the LNG 906,
producing the
final LNG product. The final LNG product may be flowed from the hydrocarbon
processing
system 900 to a desired destination using a pump 940.
[0123] It is to be understood that the process flow diagram of Fig. 9 is
not intended to
indicate that the hydrocarbon processing system 900 is to include all the
components shown in
Fig. 9. Further, the hydrocarbon processing system 900 may include any number
of additional
components not shown in Fig. 9, depending on the details of the specific
implementation.
[0124] Figs. 10A and 10B are process flow diagrams of a hydrocarbon
processing system
1000 including an SMR cycle 1002, an NRU 1004, and a methane autorefrigeration
system
1006. In various embodiments, the hydrocarbon processing system 1000 is used
to produce
LNG 1008 from a natural gas stream 1010.
[0125] As shown in Fig. 10A, the natural gas stream 1010 is flowed into
a pipe joint 1012
within the hydrocarbon processing system 1000. The pipe joint 1012 combines
the natural gas
stream 1010 with another natural gas stream. The combined natural gas stream
is compressed
within a first compressor 1014 and flowed into another pipe joint 1016 via
line 1018.
[0126] The pipe joint 1016 splits the natural gas stream into two
separate natural gas streams.
A first natural gas stream is combined with another natural gas stream via a
pipe joint 1020 and
then flowed out of the hydrocarbon processing system 1000 as fuel 1022. A
second natural gas
stream is chilled within a first chiller 1024 and flowed into another pipe
joint 1026. The pipe
joint 1026 splits the natural gas stream into two separate natural gas
streams. A first natural gas
stream is flowed into a first heat exchanger 1028 within the SMR cycle 1002
via line 1030. A
second natural gas stream is flowed into a second heat exchanger 1032 via line
1034.
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[0127] Within the first heat exchanger 1028, the natural gas stream is
cooled via indirect heat
exchange with a circulating mixed fluorocarbon refrigerant stream. From the
first heat
exchanger 1028, the mixed fluorocarbon refrigerant stream is flowed to an
expansion device
1036, such as an expansion valve or hydraulic expander, via line 1038, and is
expanded across
the expansion device 1036 isenthalpically. On expansion, some vaporization
occurs, creating a
chilled mixed fluorocarbon refrigerant stream that includes both vapor and
liquid. The chilled
mixed fluorocarbon refrigerant stream is flowed back to the first heat
exchanger 1028 and is used
to aid in the cooling of the natural gas stream within the first heat
exchanger 1028. As the
natural gas stream exchanges heat with the chilled mixed fluorocarbon
refrigerant stream, the
chilled mixed fluorocarbon refrigerant stream vaporizes, creating a vapor
mixed fluorocarbon
refrigerant stream.
[0128] The vapor mixed fluorocarbon refrigerant is then compressed
within a second
compressor 1040 and partially condensed within a second chiller 1042. The
condensed mixed
fluorocarbon refrigerant is then flowed into a first flash drum 1044 via line
1046. The flash
drum separates the partially condensed mixed fluorocarbon refrigerant stream
into a vapor mixed
fluorocarbon refrigerant stream and a liquid mixed fluorocarbon refrigerant.
The vapor mixed
fluorocarbon refrigerant stream is compressed within a third compressor 1048
and flowed into a
pipe joint 1050. The liquid mixed fluorocarbon refrigerant stream is pumped
into the pipe joint
1050 via a pump 1052.
[0129] Within the pipe joint 1050, the vapor and liquid mixed fluorocarbon
refrigerant
streams are recombined. The recombined mixed fluorocarbon refrigerant stream
is further
cooled within a third chiller 1053 and flowed back into the first heat
exchanger 1028. Within the
first heat exchanger 1028, the recombined mixed fluorocarbon refrigerant
stream is fully
condensed and sub-cooled, and is then flowed back to the expansion device 1036
via line 1038.
[0130] From the first heat exchanger 1028, the resulting LNG stream is
flowed into a pipe
joint 1054, in which it is combined with an LNG stream from the second heat
exchanger 1032.
The combined LNG stream is then flowed into the NRU 1004 via line 1056 to
remove excess
nitrogen from the LNG stream. Specifically, the LNG stream is flowed into a
reboiler 1058,
which decreases the temperature of the LNG stream. The cooled LNG stream may
be expanded
within a hydraulic expansion turbine 1060 and flowed through an expansion
device 1062, such
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as an expansion valve or hydraulic expander, which lowers the temperature and
pressure of the
LNG stream.
[0131] The LNG stream is flowed into a cryogenic fractionation column
1064, such as an
NRU tower, within the NRU 1004. In addition, heat is transferred to the
cryogenic fractionation
column 1064 from the reboiler 1058 via line 1066. The cryogenic fractionation
column 1064
separates nitrogen from the LNG stream via a cryogenic distillation process.
An overhead
stream is flowed out of the cryogenic fractionation column 1064 via line 1068.
The overhead
stream may include primarily methane, nitrogen, and other low boiling point or
non-condensable
gases, such as helium, which have been separated from the LNG stream.
[0132] The overhead stream is flowed into a reflux condenser 1070 via line
1068. Within the
reflux condenser 1070, the overhead stream is cooled via indirect heat
exchange with an LNG
stream. The heated overhead stream is then flowed into a reflux separator
1072. The reflux
separator 1072 separates any liquid within the overhead stream and returns the
liquid to the
cryogenic fractionation column 1064 as reflux. The separation of the liquid
from the overhead
stream via the reflux separator 1072 results in the production of a vapor
stream. The vapor
stream may be a fuel stream including primarily nitrogen and other low boiling
point gases.
From the reflux separator 1072, the vapor stream is flowed through the second
heat exchanger
1032 via line 1074. The vapor stream is compressed within a fourth compressor
1076, chilled
within a fourth chiller 1078, further compressed within a fifth compressor
180, and further
chilled within a fifth chiller 1082. The fuel stream is then combined with the
other natural gas
stream within the pipe joint 1020 and flowed out of the hydrocarbon processing
system 1000 as
fuel 1022.
[0133] The bottoms stream that is produced within the cryogenic
fractionation column 1064
includes primarily LNG with traces of nitrogen. The LNG stream is flowed into
the reflux
condenser 1070 and is used to cool the overhead stream from the cryogenic
fractionation column
1064. As the LNG stream exchanges heat with overhead stream, it is partially
vaporized,
producing a multiphase natural gas stream.
[0134] The multiphase natural gas stream is flowed into a second flash
drum 1084 via line
1083. The second flash drum 1084 separates the multiphase natural gas stream
into a natural gas
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stream and an LNG stream. The natural gas stream is combined within another
natural gas
stream within a pipe joint 1086, compressed within a sixth compressor 1087,
and combined with
the initial natural gas stream 1010 within the pipe joint 1012.
[0135] From the second flash drum 1084, the LNG stream is flowed through
an expansion
device 1088, such as an expansion valve or hydraulic expander, that controls
the flow of the
natural gas stream into a third flash drum 1089. The expansion device 1088
reduces the
temperature and pressure of the natural gas stream, resulting in the flash
evaporation of the
natural gas stream into both a natural gas stream and an LNG stream. The
natural gas stream is
then separated from the LNG steam via the third flash drum 1089.
[0136] The natural gas stream is flowed from the third flash drum 1089 into
a pipe joint
1090, in which the natural gas stream is combined with another natural gas
stream. The
combined natural gas stream is compressed within a seventh compressor 1091 and
then flowed
into the pipe joint 1086.
[0137] From the third flash drum 1089, the LNG stream is flowed through
an expansion
device 1092, such as an expansion valve or hydraulic expander, that controls
the flow of the
natural gas stream into a fourth flash drum 1093. The expansion device 1092
reduces the
temperature and pressure of the natural gas stream, resulting in the flash
evaporation of the
natural gas stream into both a natural gas stream and an LNG stream. The
natural gas stream is
then separated from the LNG steam via the fourth flash drum 1093.
[0138] The natural gas stream is flowed from the fourth flash drum 1093
into a pipe joint
1094, in which the natural gas stream is combined with another natural gas
stream. The
combined natural gas stream is compressed within an eighth compressor 1095 and
flowed into
the pipe joint 1090.
[0139] The LNG stream is flowed into an LNG taffl( 1096. The LNG taffl(
1096 may store
the LNG stream for any period of time. Boil-off gas generated within the LNG
taffl( 1096 is
flowed to the pipe joint 1094 and combined within the natural gas stream from
the fourth flash
drum 1093. At any point in time, the final LNG stream 1008 may be transported
to a LNG
tanker 1097 using a pump 1098, for transport to markets. Additional boil-off
gas 1099 generated
while loading the final LNG stream 1008 into the LNG tanker 1097 may be
recovered in the
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hydrocarbon processing system 1000.
[0140] It is to be understood that the process flow diagrams of Figs.
10A and 10B are not
intended to indicate that the hydrocarbon processing system 1000 is to include
all the
components shown in Figs. 10A and 10B. Further, the hydrocarbon processing
system 1000
may include any number of additional components not shown in Figs. 10A and
10B, depending
on the details of the specific implementation.
[0141] Figs. 11A and 11B are process flow diagrams of a hydrocarbon
processing system
1100 including an economized DMR cycle 1102, an NRU 1104, and a methane
autorefrigeration
system 1106. In various embodiments, the hydrocarbon processing system 1100 is
used to
produce LNG 1108 from a natural gas stream 1110.
[0142] As shown in Fig. 11A, the natural gas stream 1110 is flowed into
a pipe joint 1112
within the hydrocarbon processing system 1100. The pipe joint 1112 splits the
natural gas
stream 110 into three separate natural gas streams. A first natural gas stream
is flowed to a pipe
joint 1114 via line 1116. Within the pipe joint 1114, the first natural gas
stream is combined
with another stream including natural gas, and the combined stream is flowed
out of the
hydrocarbon processing system 1100 as fuel 1118.
[0143] From the pipe joint 1112, a second natural gas stream is flowed
into the NRU 1104.
Within the NRU 1104, the natural gas stream is cooled within a first heat
exchanger 1120 and
combined with an LNG stream exiting the economized DMR cycle 1102 within a
pipe joint
1122.
[0144] Furthermore, a third natural gas stream is flowed from the pipe
joint 1112 to another
pipe joint 1124 as the main feed stream. Within the pipe joint 1124, the
natural gas stream is
combined with another natural gas stream from the methane autorefrigeration
system 1106. The
combined natural gas stream is then cooled within the economized DMR cycle
1102.
Specifically, the natural gas stream is cooled using a second heat exchanger
1126, a third heat
exchanger 1128, and a fourth heat exchanger 1130 within a warm MR cycle of the
economized
DMR cycle 1102. The natural gas stream is further cooled using a fifth heat
exchanger 1132 and
a sixth heat exchanger 1134 within a cold MR cycle of the economized DMR cycle
1102.
[0145] Within the second heat exchanger 1126, the natural gas stream is
cooled via indirect
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heat exchange with a circulating warm fluorocarbon refrigerant stream. From
the second heat
exchanger 1126, the warm fluorocarbon refrigerant stream is flowed into a pipe
joint 1140, in
which it is combined with another warm fluorocarbon refrigerant stream from
the third and
fourth heat exchangers 1128 and 1130.
[0146] From the pipe joint 1140, the warm fluorocarbon refrigerant stream
is compressed
within a compressor 1142 and chilled within a chiller 1144. The warm
fluorocarbon refrigerant
stream is then flowed through the second heat exchanger 1126. Within the
second heat
exchanger 1126, the warm fluorocarbon refrigerant stream is sub-cooled via
indirect heat
exchange. From the second heat exchanger 1126, the sub-cooled fluorocarbon
refrigerant stream
is flowed to a pipe joint 1148, which splits the fluorocarbon refrigerant
stream into two
fluorocarbon refrigerant streams. A first fluorocarbon refrigerant stream is
flowed through an
expansion device 1150 and back into the second heat exchanger 1126. Within the
second heat
exchanger 1126, the fluorocarbon refrigerant stream cools the natural gas
stream and the other
fluorocarbon refrigerant streams flowing through the second heat exchanger
1126. The
fluorocarbon refrigerant stream is then flowed into the pipe joint 1140.
[0147] A second fluorocarbon refrigerant stream is flowed from the pipe
joint 1150 into the
third heat exchanger 1128 via line 1152. Within the third heat exchanger 1128,
the fluorocarbon
refrigerant stream is further chilled and sub-cooled via indirect heat
exchange. From the third
heat exchanger 1128, the sub-cooled fluorocarbon refrigerant stream is flowed
to a pipe joint
1153, which splits the fluorocarbon refrigerant stream into two fluorocarbon
refrigerant streams.
A first fluorocarbon refrigerant stream is flowed through an expansion device
1154 and back into
the third heat exchanger 1128. Within the third heat exchanger 1128, the
fluorocarbon
refrigerant stream cools the natural gas stream and the other fluorocarbon
refrigerant streams
flowing through the third heat exchanger 1128. The fluorocarbon refrigerant
stream is then
flowed into a pipe joint 1156, in which it is combined with another warm
fluorocarbon
refrigerant stream from the fourth heat exchanger 1130. From the pipe joint
1156, the combined
warm fluorocarbon refrigerant stream is compressed within a compressor 1158,
chilled within a
chiller 1159, and flowed into the pipe joint 1140 to be combined with the
fluorocarbon
refrigerant stream exiting the second heat exchanger 1126.
[0148] A second fluorocarbon refrigerant stream is flowed from the pipe
joint 1153 into the
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fourth heat exchanger 1130 via line 1160. Within the fourth heat exchanger
1130, the
fluorocarbon refrigerant stream is further chilled and sub-cooled via indirect
heat exchange.
From the fourth heat exchanger 1130, the sub-cooled fluorocarbon refrigerant
stream is flowed
through an expansion device 1161 and back into the fourth heat exchanger 1130.
Within the
fourth heat exchanger 1130, the fluorocarbon refrigerant stream cools the
natural gas stream and
the other fluorocarbon refrigerant streams flowing through the fourth heat
exchanger 1130. The
fluorocarbon refrigerant stream is then compressed within a compressor 1163
and flowed into
the pipe joint 1156 to be combined with the fluorocarbon refrigerant stream
exiting the third heat
exchanger 1128.
[0149] In various embodiments, a fluorocarbon refrigerant stream from the
cold MR cycle of
the economized DMR cycle 1102 is flowed through the second heat exchanger
1126, the third
heat exchanger 1128, and the fourth heat exchanger 1130 within the warm MR
cycle via line
1164. Within the second heat exchanger 1126, the third heat exchanger 1128,
and the fourth heat
exchanger 1130, the fluorocarbon refrigerant stream from the cold MR cycle is
cooled and
condensed via indirect heat exchange with the fluorocarbon refrigerant within
the warm MR
cycle. The cold, liquid fluorocarbon refrigerant stream exiting the fourth
heat exchanger 1130 is
flowed into the fifth heat exchanger 1132 of the cold MR cycle via line 1165.
[0150] Within the fifth heat exchanger 1132, the cold fluorocarbon
refrigerant stream is
further sub-cooled via indirect heat exchange. From the fifth heat exchanger
1132, the sub-
cooled fluorocarbon refrigerant stream is flowed to a pipe joint 1166, which
splits the
fluorocarbon refrigerant stream into two fluorocarbon refrigerant streams. A
first fluorocarbon
refrigerant stream is flowed through an expansion device 1167 and back into
the fifth heat
exchanger 1132. Within the fifth heat exchanger 1132, the fluorocarbon
refrigerant stream cools
the natural gas stream and the incoming liquid fluorocarbon refrigerant stream
1165. The
fluorocarbon refrigerant stream is then flowed into a pipe joint 1168, in
which it is combined
with a fluorocarbon refrigerant stream from the sixth heat exchanger 1134. The
combined
fluorocarbon refrigerant stream is compressed within a compressor 1169,
chilled within a chiller
1170, and flowed back into the warm MR cycle of economized DMR cycle 1102 via
line 1164.
[0151] A second fluorocarbon refrigerant stream is flowed from the pipe
joint 1166 into the
sixth heat exchanger 1134 via line 1171. Within the sixth heat exchanger 1134,
the fluorocarbon
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refrigerant stream is further chilled and sub-cooled via indirect heat
exchange. From the sixth
heat exchanger 1134, the fluorocarbon refrigerant stream is flowed through an
expansion valve
1172 and back into the sixth heat exchanger 1134. Within the sixth heat
exchanger 1134, the
fluorocarbon refrigerant stream cools the natural gas stream, producing an LNG
stream, and
chills the liquid fluorocarbon refrigerant stream. The fluorocarbon
refrigerant stream is then
compressed within a compressor 1173 and flowed into the pipe joint 1168, in
which it is
combined with the fluorocarbon refrigerant stream exiting the fifth heat
exchanger 1132.
[0152] From the sixth heat exchanger 1134, the resulting LNG stream is
flowed out of the
economized DMR cycle 1102 and into the NRU 1104 via line 1174. Specifically,
the LNG
stream is flowed into the pipe joint 1122, in which it is combined with the
natural gas stream
exiting the first heat exchanger 1120. The LNG stream is then flowed into a
reboiler 1175,
which decreases the temperature of the LNG stream. The cooled LNG stream may
be expanded
within a hydraulic expansion turbine 1176 and flowed through an expansion
device 1177, such
as an expansion valve or hydraulic expander, which lowers the temperature and
pressure of the
LNG stream.
[0153] The LNG stream is flowed into a cryogenic fractionation column
1178, such as an
NRU tower, within the NRU 1104. In addition, heat is transferred to the
cryogenic fractionation
column 1178 from the reboiler 1175 via line 1179. The cryogenic fractionation
column 1178
separates nitrogen from the LNG stream via a cryogenic distillation process.
An overhead
stream is flowed out of the cryogenic fractionation column 1178 via line 1180.
The overhead
stream may include primarily methane, nitrogen, and other low boiling point or
non-condensable
gases, such as helium, which have been separated from the LNG stream.
[0154] The overhead stream is flowed into a reflux condenser 1181.
Within the reflux
condenser 1181, the overhead stream is cooled via indirect heat exchange with
an LNG stream.
The heated overhead stream is then flowed into a reflux separator 1182. The
reflux separator
1182 separates any liquid within the overhead stream and returns the liquid to
the cryogenic
fractionation column 1178 as reflux. The separation of the liquid from the
overhead stream via
the reflux separator 1182 results in the production of a vapor stream. The
vapor stream may be a
fuel stream including primarily nitrogen and other low boiling point gases.
From the reflux
separator 1182, the vapor stream is flowed through the first heat exchanger
1120. The vapor
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stream is then progressively compressed and chilled within a first compressor
1183, a first chiller
1184, a second compressor 1185, and a second chiller 1186. The compressed,
chilled stream is
then combined with a natural gas stream within the pipe joint 1114, and the
combined stream is
flowed out of the hydrocarbon processing system 1100 as fuel 1118.
[0155] The bottoms stream that is produced within the cryogenic
fractionation column 1178
includes primarily LNG with traces of nitrogen. The LNG is flowed through the
reflux
condenser 1181 and is used to cool the overhead stream from the cryogenic
fractionation column
1178. As the LNG stream exchanges heat with the overhead stream, it is
partially vaporized,
producing a multiphase natural gas stream.
[0156] The multiphase natural gas stream is flowed into a third flash drum
1187, which
separates the multiphase natural gas stream into a natural gas stream and an
LNG stream. The
natural gas stream is combined within another natural gas stream within a pipe
joint 1188,
compressed within a compressor 1189, chilled within a chiller 1190, and
combined with the
initial natural gas stream within the pipe joint 1124.
[0157] From the third flash drum 1187, the LNG stream is flowed through an
expansion
device 1191, such as an expansion valve or hydraulic expander, that controls
the flow of the
natural gas stream into a fourth flash drum 1192. The expansion device 1191
reduces the
temperature and pressure of the natural gas stream, resulting in the flash
evaporation of the
natural gas stream into both a natural gas stream and an LNG stream. The
natural gas stream is
then separated from the LNG steam via the fourth flash drum 1192.
[0158] The natural gas stream is flowed from the fourth flash drum 1192
into a pipe joint
1193, in which the natural gas stream is combined with another natural gas
stream. The
combined natural gas stream is compressed within a compressor 1194 and then
flowed into the
pipe joint 1188 to be combined with the natural gas stream from the third
flash drum 1187.
[0159] From the fourth flash drum 1192, the LNG stream is flowed into an
LNG taffl( 1195.
The LNG taffl( 1195 may store the LNG stream for any period of time. Boil-off
gas generated
within the LNG taffl( 1195 is flowed to the pipe joint 1193 and combined
within the natural gas
stream from the fourth flash drum 1192. At any point in time, the final LNG
stream 1108 may
be transported to a LNG tanker 1196 using a pump 1197, for transport to
markets. Additional
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boil-off gas 1198 generated while loading the final LNG stream 1108 into the
LNG tanker 1196
may be recovered in the hydrocarbon processing system 1100.
Method for LNG Production
[0160] Fig. 12 is a process flow diagram of a method 1200 for the
formation of LNG from a
natural gas stream using a mixed fluorocarbon refrigerant. The method 1200 may
be
implemented within any suitable type of hydrocarbon processing system. For
example, the
method 1200 may be implemented by any of the hydrocarbon processing systems
500 or 800-
1100 discussed with respect to Figs. 5-11.
[0161] The method 1200 begins at block 1202, at which a natural gas is
cooled to produce
LNG in a fluorocarbon refrigeration system using a mixed fluorocarbon
refrigerant. The mixed
fluorocarbon refrigerant may include any suitable mixture of fluorocarbon
components, or any
suitable mixture of fluorocarbon components and other non-flammable
components, such as inert
compounds. For example, the mixed fluorocarbon refrigerant may be a mixture of
any number
of different HFCs, HF0s, and/or inert compounds.
[0162] Cooling the natural gas in the fluorocarbon refrigeration system may
include
compressing the mixed fluorocarbon refrigerant to provide a compressed mixed
fluorocarbon
refrigerant and cooling the compressed mixed fluorocarbon refrigerant by
indirect heat exchange
with a cooling fluid to provide a cooled mixed fluorocarbon refrigerant. The
cooled mixed
fluorocarbon refrigerant may then be passed to a heat exchange area, and the
natural gas may be
cooled by indirect heat exchange with the cooled mixed fluorocarbon
refrigerant in the heat
exchange area.
[0163] The fluorocarbon refrigeration system may be any suitable type of
refrigeration
system that is capable of cooling a natural gas stream using a mixed
fluorocarbon refrigerant.
For example, the fluorocarbon refrigeration system may be an SMR cycle, DMR
cycle, TMR
cycle, or pre-cooled MR cycle. If the fluorocarbon refrigeration system is a
DMR cycle, for
example, the fluorocarbon refrigeration system may include a first MR cycle
that uses a warm
mixed fluorocarbon refrigerant and a second MR cycle that uses a cold mixed
fluorocarbon
refrigerant. The first mixed refrigerant cycle and the second mixed
refrigerant cycle may be
connected in series.
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[0164] At block 1204, nitrogen is removed from the LNG in an NRU. In
some
embodiments, the nitrogen stream separated from the natural gas via the NRU is
used to further
cool at least a portion of the natural gas.
[0165] In various embodiments, the natural gas is further cooled to
produce the LNG in an
autorefrigeration system. The autorefrigeration system may include a number of
expansion
devices and flash drums for cooling the natural gas. In addition, in some
embodiments, the
natural gas is further cooled to produce the LNG in a nitrogen refrigeration
system using a
nitrogen refrigerant. The nitrogen refrigeration system may be located
upstream of the
autorefrigeration system, for example.
[0166] It is to be understood that the process flow diagram of Fig. 12 is
not intended to
indicate that the blocks of the method 1200 are to be executed in any
particular order, or that all
of the blocks are to be included in every case. Further, any number of
additional blocks may be
included within the method 1200, depending on the details of the specific
implementation.
Embodiments
[0167] Embodiments of the techniques may include any combinations of the
methods and
systems shown in the following numbered paragraphs. This is not to be
considered a complete
listing of all possible embodiments, as any number of variations can be
envisioned from the
description herein.
1. A hydrocarbon processing system for liquefied natural gas (LNG)
production,
including:
a fluorocarbon refrigeration system configured to cool a natural gas to
produce LNG
using a mixed fluorocarbon refrigerant; and
a nitrogen rejection unit (NRU) configured to remove nitrogen from the LNG.
2. The hydrocarbon processing system of paragraph 1, including a nitrogen
refrigeration system configured to further cool the natural gas to produce the
LNG using a
nitrogen refrigerant.
3. The hydrocarbon processing system of any of paragraphs 1 or 2, including
an
autorefrigeration system configured to further cool the natural gas to produce
the LNG.
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4. The hydrocarbon processing system of paragraph 3, wherein the
autorefrigeration
system includes a number of flash drums and a number of expansion devices.
5. The hydrocarbon processing system of any of paragraphs 1-3, wherein at
least a
portion of the natural gas is cooled using a nitrogen stream separated from
the natural gas via the
NRU.
6. The hydrocarbon processing system of any of paragraphs 1-3 or 5, wherein
the
fluorocarbon refrigeration system includes a single mixed refrigerant cycle.
7. The hydrocarbon processing system of any of paragraphs 1-3, 5, or 6,
wherein the
fluorocarbon refrigeration system includes a pre-cooled mixed refrigerant
cycle.
8. The hydrocarbon processing system of any of paragraphs 1-3 or 5-7,
wherein the
fluorocarbon refrigeration system includes a dual mixed refrigerant cycle.
9. The hydrocarbon processing system of paragraph 8, wherein the dual mixed
refrigerant cycle includes:
a first mixed refrigerant cycle that uses a warm mixed fluorocarbon
refrigerant; and
a second mixed refrigerant cycle that uses a cold mixed fluorocarbon
refrigerant, wherein
the first mixed refrigerant cycle and the second mixed refrigerant cycle are
connected in series.
10. The hydrocarbon processing system of any of paragraphs 1-3 or 5-8,
wherein the
fluorocarbon refrigeration system includes a triple mixed refrigerant cycle.
11. The hydrocarbon processing system of any of paragraphs 1-3, 5-8, or 10,
wherein
the fluorocarbon refrigeration system includes a heat exchanger configured to
allow for cooling
of the natural gas via an indirect exchange of heat between the natural gas
and the mixed
fluorocarbon refrigerant.
12. The hydrocarbon processing system of any of paragraphs 1-3, 5-
8, 10, or 11,
wherein the fluorocarbon refrigeration system includes:
a compressor configured to compress the mixed fluorocarbon refrigerant to
provide a
compressed mixed fluorocarbon refrigerant;
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a chiller configured to cool the compressed mixed fluorocarbon refrigerant to
provide a
cooled mixed fluorocarbon refrigerant; and
a heat exchanger configured to cool the natural gas via indirect heat exchange
with the
cooled mixed fluorocarbon refrigerant.
13. The
hydrocarbon processing system of any of paragraphs 1-3, 5-8, or 10-12,
wherein the hydrocarbon processing system is configured to chill the natural
gas for hydrocarbon
dew point control.
14. The hydrocarbon processing system of any of paragraphs 1-3, 5-8, or 10-
13,
wherein the hydrocarbon processing system is configured to chill the natural
gas for natural gas
liquid extraction.
15. The hydrocarbon processing system of any of paragraphs 1-3, 5-8, or 10-
14,
wherein the hydrocarbon processing system is configured to separate methane
and lighter gases
from carbon dioxide and heavier gases.
16. The hydrocarbon processing system of any of paragraphs 1-3, 5-8, or 10-
15,
wherein the hydrocarbon processing system is configured to prepare
hydrocarbons for liquefied
petroleum gas production storage.
17. The hydrocarbon processing system of any of paragraphs 1-3, 5-8, or 10-
16,
wherein the hydrocarbon processing system is configured to condense a reflux
stream.
18. A method for liquefied natural gas (LNG) production, including:
cooling a natural gas to produce LNG in a fluorocarbon refrigeration system
using a
mixed fluorocarbon refrigerant; and
removing nitrogen from the LNG in a nitrogen rejection unit (NRU).
19. The method of any of paragraphs 18, including further cooling the
natural gas to
produce the LNG in a nitrogen refrigeration system using a nitrogen
refrigerant.
20. The
method of any of paragraphs 18 or 19, including further cooling the natural
gas to produce the LNG in an autorefrigeration system.
21. The
method of paragraph 20, including cooling at least a portion of the natural
gas
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using a nitrogen stream separated from the natural gas via the NRU.
22. The method of any of paragraphs 18-20, wherein cooling the natural gas
in the
fluorocarbon refrigeration system includes:
compressing the mixed fluorocarbon refrigerant to provide a compressed mixed
fluorocarbon refrigerant;
cooling the compressed mixed fluorocarbon refrigerant by indirect heat
exchange with a
cooling fluid to provide a cooled mixed fluorocarbon refrigerant;
passing the cooled mixed fluorocarbon refrigerant to a heat exchange area; and
heat exchanging the natural gas with the cooled mixed fluorocarbon refrigerant
in the
heat exchange area.
23. A hydrocarbon processing system for formation of a liquefied natural
gas (LNG),
including:
a mixed refrigerant cycle configured to cool a natural gas using a mixed
fluorocarbon
refrigerant, wherein the mixed refrigerant cycle includes a heat exchanger
configured to allow for cooling of the natural gas via an indirect exchange of
heat
between the natural gas and the mixed fluorocarbon refrigerant;
a nitrogen rejection unit (NRU) configured to remove nitrogen from the natural
gas; and
a methane autorefrigeration system configured to cool the natural gas to
produce the
LNG.
24. The hydrocarbon processing system of paragraph 23, wherein the mixed
fluorocarbon refrigerant includes a mixture of two or more hydrofluorocarbon
refrigerants.
25. The hydrocarbon processing system of any of paragraphs 2 or 24, wherein
a
nitrogen stream separated from the natural gas via the NRU is used to cool at
least a portion of
the natural gas.
26. The hydrocarbon processing system of any of paragraphs 23-25, wherein
the
methane autorefrigeration system includes a number of expansion devices and a
number of flash
drums.
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[0168] While the present techniques may be susceptible to various
modifications and
alternative forms, the embodiments discussed herein have been shown only by
way of example.
However, it should again be understood that the techniques is not intended to
be limited to the
particular embodiments disclosed herein. Indeed, the present techniques
include all alternatives,
modifications, and equivalents falling within the true spirit and scope of the
appended claims.
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